Integrated heated prevaporation module

ABSTRACT

An integrated heating system for adding heat to a feed fuel within a module by way of an integrated heating element within the body or casing of the module. The heat may be selectively added to maintain a selected temperature.

RELATED APPLICATION

This application is a Continuation application of U.S. application Ser.No. 11/345,980 titled “Multi-Stage Sulfur Removal System and Process foran Auxiliary Fuel System”, filed Feb. 1, 2006, and possibly US utilityincorporated by reference herein in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of Endeavor

This disclosure relates generally to fuel systems and more particularlyto a system and process for extraction of an auxiliary fuel stream withlow concentrations of sulfur compounds from a primary fuel stream havinghigher concentrations of sulfur compounds including an internally heatedmodule.

2. Description of Related Art

Continuing improvements in the performance, cost and durability of fuelcell systems have continued to raise interest in their use as auxiliarypower units (APU), for example, in a vehicle such as a hybrid or fuelcell powered automobile. One limitation to their practical applicationinvolves the logistic fuels or conventional fuels used, for example,diesel and kerosene cuts. These fuels have sulfur content in the rangeof 30 to 3,000 ppm, which either impacts the conversion of these fuelsto hydrogen or the synthetic gas stream, or impacts the performance ofthe fuel cell downstream. One alternative is to require a synthetic “nosulfur” type liquid fuel such as Fischer-Tropsch liquid or gas-to-liquidproducts for the APU, but this forces the need for two separate fuelstreams to be provided for the same vehicle.

Some governmental agencies of the United States for example, havemandated lower levels of sulfur in fuels such as the recent push toward30 to 300 ppm. Even with levels near the lowest limit, the sulfurcontent affects the performance of catalysts in down stream processes,and therefore, preventing effective use of fuel cell systems.Technologies, including membrane based technologies, are being developedfor refinery scale applications to achieve these lower sulfurspecifications. Membrane technologies and specifically prevaporationmembrane technology are commercial technologies that are practiced in anumber of industries for the separation of higher vapor pressurecomponents from a mixture of liquid stream.

Typical prevaporation assemblies operate from about 90° to about 130° C.and permeate flux generally increases with increasing temperature (heatcauses membrane swelling. A vaporizes permeate, upon entering a vacuumspace within an assembly, losses heat needed for phase to the leaf (orlayered) material of the assembly, as the vapor passes through thelength of the assembly. Once the feed solution has cooled significantly,the membrane generally contracts thereby becoming resistant to diffusionwhich reduces the membrane module fractionation efficiency/capacity.

U.S. Pat. No. 5,445,731 describes reheating retentate external to theapparatus before reintroducing it into a second membrane module.

Plate and frame designs heating elements are described in U.S. Pat. No.4,650,574 to provide heating within a membrane assemblies which havethermal resistance between the heating media and the feed solution.

It would be desirable to have a simple process that provides the neededseparation selectivity, that could be implemented in a compact,inexpensive system and that would operate with a wide range of primaryfuels from gasoline, kerosene, jet fuel and diesel or water-solublemixtures. It is to these needs that the present disclosure is directed.

SUMMARY OF THE DISCLOSURE

Embodiments of a system and process for producing an auxiliary fuelstream containing low concentration of sulfur compounds from a primaryfuel stream according to an exemplary implementation are disclosed. Thesystem includes a first separation stage that isolates a stage-onepermeate stream and a stage-one retentate stream from a portion of theprimary fuel stream. A second separation stage isolates a stage-twopermeate stream and a stage-two retentate stream from the stage-onepermeate stream in which the stage-two retentate stream includes anauxiliary fuel stream containing low concentrations of sulfur compounds.The stage-one retentate stream and the stage-two permeate stream aremixed and returned into the primary fuel stream. The result is anauxiliary fuel stream containing low concentration of sulfur compoundsalong with the primary fuel stream.

According to a further exemplary implementation, a process forseparating an auxiliary fuel stream containing low sulfur compounds froma primary fuel stream includes: isolating a stage-one permeate streamand a stage-one retentate stream from the primary fuel stream;evaporating the stage-one permeate stream at a vacuum; isolating astage-two permeate stream and a stage-two retentate stream from thestage-one permeate stream, the stage-two retentate stream comprising afuel stream containing low concentrations of sulfur compounds; andevaporating the stage-two permeate stream at a vacuum for return of thestage-two permeate stream to the primary fuel stream. The stage-tworetentate stream is therefore the auxiliary fuel stream containing lowsulfur compounds.

According to an additional exemplary implementation, a system forseparating a fuel stream containing low concentrations of sulfurcompounds from a primary fuel stream includes: a fuel supply; astage-one separator; a stage-two separator; a first supply lineconnecting the fuel supply to the stage-one separator; a second supplyline connecting the stage-one separator and the stage-two separator. Thefirst supply line conveys a fuel stream from the fuel supply to thestage-one separator. The stage-one separator produces a stage-onepermeate stream and a stage-one retentate stream from the stage-one fuelsupply stream. The second supply line conveys the stage-one permeatestream from the stage-one separator, to the stage-two separator. Thestage-two separator produces a stage-two permeate stream and a stage-tworetentate stream. The stage-two retentate stream produced is fuel streamcontaining low concentrations of sulfur compounds. In this system, thestage-one retentate stream and stage-two permeate are then mixed andreturned to the primary fuel stream.

According to still further exemplary implementation, a system forseparating a fuel stream containing low concentration of sulfurcompounds from a primary fuel stream is disclosed that includes: astage-one separator providing a gaseous stage-one permeate stream and astage-one retentate stream from a primary fuel stream; a first eductorassociated with the stage-one separator, the eductor providing a vacuumand cooling energy to condense the stage-one permeate vapor using thecooled stage-one permeate liquid as the motive fluid for the firsteductor; and a stage-two separator providing a stage-two retentatestream and a gaseous stage-two permeate stream from the condensedstage-one permeate stream, the stage-two retentate stream comprisingfuel stream containing low concentration of sulfur compounds; and asecond eductor associated with the stage-two separator, the eductorusing the cooled stage-one retentate as the motive fluid to provide avacuum for stage-two permeate vapor and condense and mix the stage-twopermeate vapor with the stage-one retentate. The vacuum produced may notonly be generated by the use of eductors with process liquid as motivefluid. Compressed gases such as air, steam or N₂ enriched air may beused as the motive fluid. Alternatively, a motor-driven vacuum pump maybe utilized to generate the vacuum.

According to an additional exemplary implementation, a system forseparating a fuel stream containing low concentrations of sulfurcompounds from a primary fuel stream includes: a fuel supply; astage-one separator; a reactive de-sulfurization catalyst; a sorbent beddownstream of the catalyst; a first supply line connecting the fuelsupply to the stage-one separator; a first vapor phase supply lineconnecting the stage-one separator to the reactive de-sulfurizationcatalyst; a first sorbent bed feed line; a first condensed supply line;and a first reactant supply line. The first supply line conveys a fuelstream from the fuel supply to the stage-one separator. The stage-oneseparator produces a stage-one permeate stream and a stage-one retentatestream from the stage-one fuel supply stream. The first vapor phasesupply line conveys the stage-one permeate stream from the stage-oneseparator, to the reactive de-sulfurization catalyst. The reactantsupply line supplies reactant to the reactive de-sulfurization catalyst.The catalyst supports the chemical reaction of the sulfur species in thestage one permeate with the reactant to modify the sulfur species. Thefirst sorbent bed feed lines connects the reactant catalyst with thesorbent bed. The modified sulfur species adsorb or absorb to the sorbentand the remaining stage one permeate is condensed for later use orprocessing.

In one exemplary implementation membrane module inefficiency isaddressed by placing a compensating heat element precisely where it isneeded in direct contact with the feed inside the layered or “leaf”arrangement wherein a hot fuel feed stream is separated into permeateand retentate. The layers may be used to form a chamber or channelthrough which the hot fuel is fed. The membrane module's internaltemperature is impacted by the heat element to replace some of the lossof heat from the vaporized feed fuel as it travels over the entirelength of the module.

In one aspect the vaporized feed fuel need not be reheated to the samedegree, or at all, before passing through a module because the internalheating strategy within the module compensates for at least of portionof heat losses attributable to the passing of the vaporized feed fuelthrough a membrane module, such as a prevaporation module. Those ofordinary skill in the art will recognize that this strategy may beapplied to a variety of different modules wherein maintaining atemperature state is important. In some exemplary implementations themodule is tubular and the leaf arrangement is spiral or wound. In otherexemplary implementations the layered arrangement may be planar such asin a plate and frame assembly wherein the feed fuel passes through achamber or channel.

The source of energy to the module may be provided by an electricheating blanket sealed within the module's feed channels.

The source of energy to the module may be provided by a thin hollow foilwrapping, and or sealed within the module's feed spacing through which aheat-exchange fluid can provide the heat necessary for vaporization.

The source of energy to the heat element may be provided by a solidmetal foil wrapping, and or sealed within a module to control theintroduction of RF (radiofrequency) energy used to heat the foil bywrapping an induction coil around the module assembly. Through thiscoil, an AC current would induce a magnetic field thereby heating thefoils within the leaf space. Additionally the induction element can beplaced inside the module's core tube to induce the magnetic field fromwithin the spiral wrappings.

The source of energy to the heat element may be provided by aninductively driven electrical conduit using either electricity or radiofrequency.

To note one example of the latent heat requirement for PV systems inhydrocarbon fuel processing, the compensating element should be able toprovide approximately 240 W per square meter of membrane (based on aflux rate of 2.5 kg/hrm²). Without this additional heat to compensatefor phase change, almost half of the enthalpy of the incoming feed willbe lost and subsequently cool by roughly 300C. Such a drastictemperature drop would force put most PV membrane materials below theirminimum operating temperature resulting in little or no permeationwhatsoever.

Many PV applications require larger fractions of raw feed material thancan be achieved with the existing single module technology. Theinvention provides an energy effective solution to this problem.

The features and aspects of the present disclosure will be betterunderstood from the following detailed descriptions, taken inconjunction with the accompanying drawings, all of which are given byillustration only, and are not limitative of the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

The above-mentioned features and objects of the present disclosure willbecome more apparent with reference to the following description takenin conjunction with the accompanying drawings wherein like referencenumerals denote like elements and in which:

FIG. 1 is a conceptual diagram of an exemplary embodiment of the processin accordance with the present disclosure.

FIG. 2 is a simplified schematic flow diagram of an embodiment of thesystem in accordance with the present disclosure.

FIG. 3 is a diagram illustrating the results of experimental tests on aperformance model of the system and process shown in FIGS. 1 and 2.

FIG. 4 is a simplified schematic flow diagram of another embodiment ofthe system in accordance with the present disclosure.

FIG. 5 is a partial schematic flow diagram of the stage-one portion ofanother embodiment of the system in which a two step condensationfunction is used on the stage-one permeate.

FIG. 6 is a chart illustrating the distillation profiles of permeate 1condensates.

FIG. 7 is a chart illustrating the sulfur concentrations of the variouscondensates.

FIG. 8 is a schematic flow diagram of another embodiment of the systemin accordance with the present disclosure.

FIG. 9 is a simplified schematic flow diagram of another embodiment ofthe system in accordance with the present disclosure.

FIG. 10 is a schematic flow diagram of an exemplary system illustrativeof a system shown in FIG. 9.

FIG. 11 is a schematic flow diagram of another exemplary systemillustrative of an alternative system shown in FIG. 9.

FIG. 12 is a schematic flow diagram of another exemplary systemillustrative of an alternative system as in FIG. 9.

FIG. 13 is a schematic flow diagram of another exemplary systemillustrative of an alternative system as in FIG. 9.

FIG. 14 is a schematic flow diagram of another exemplary systemillustrative of an alternative system as in FIG. 9.

FIG. 15 is a partially exploded view of a spiral module with integralheating.

FIG. 16 is a cutaway along line A-A of FIG. 15.

FIG. 17 is an assembly view a module with integral heating.

DEFINITIONS

In the discussion that follows, the terms used are used according totheir plain meaning as intended by a person skilled in the art. In thedescribed embodiments below, the terms below are intended to be used asfollows.

The term “hydrocarbon” is generally used to describe an organic compoundprimarily composed of hydrogen and carbon atoms of various lengths andstructures but may also contain non-carbon atoms (such as oxygen,sulfur, or nitrogen).

The term “straight chain hydrocarbon” implies that the compound is aparaffin or isoparaffin type hydrocarbon without ring structures.

The term “prevaporation” means separation of mixtures of liquids bypartial vaporation through a non-porous membrane.

The term “naphthenes or naphthenic compounds” are hydrocarbons with oneor more rings of carbon atoms with only single bonds.

The term “aromatic compound” is an hydrocarbon containing one or morerings of carbon with double bonds within these rings.

The term “heterocyclics” are aromatic or naphthenic compounds thatcontain atoms in addition to carbon and hydrogen such as sulfur,nitrogen or oxygen. Heterocyclics are usually polar in nature.

The terms “polar” or “ionic”, as referred to membranes, indicatemembranes that contain ionic bonds. Similarly, the terms “non-polar” or“non-ionic” are membranes that do not contain ionic bonds. If themembrane is polar in nature or coated with a polar material such as afluorinated polymer with branched sulfonic acid groups, e.g., Nafion®,the compounds with polar species will tend to be selectively transferredthrough the membrane. Non-polar membranes, such as cellulose triacetate,will tend to be selective to non-polar compounds and selectivelydecrease the transfer rate of ionic compounds.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure relates to a prevaporation membrane process andsystem for separating a slip stream or auxiliary fuel stream from aprimary fuel stream.

It should be appreciated that for simplicity and clarity ofillustration, elements shown in the Figures and discussed below have notnecessarily been drawn to scale. For example, the dimensions of some ofthe elements are exaggerated relative to each other for clarity.Further, where considered appropriate, reference numerals have beenrepeated among the Figures to indicate corresponding elements.

FIG. 1 shows a simplified schematic representation of the overallprocess according to this disclosure, indicating two separation stagesand the selectivity for the various elements of the fuel feed mixture.The process 1 comprises flowing a portion of a primary fuel stream 2through a stage-one separator 11 and then flowing a separated portionthrough a stage-two separator 16. The primary fuel 2 can be anycommercially available transportation or logistics fuel (such as, butnot limited to, reformulated gasoline, kerosene and diesel commonlyavailable at interstate refueling stations, jet fuels, aviationkerosene's (A-1) or military specification fuels like JP-8, NATO F-76,etc.) These fuels consist of a wide mix of hydrocarbon components, whichtypically have been separated from a bulk fuel source through a vaporfractionation process during refining. As a result, each mixture has arange of compounds that each vaporize over a defined temperature band.In general, gasoline contains lighter components than kerosene, which inturn is lighter than diesel fuels. Within each volume of fuel of aspecific type there exists a range of compounds with various vaporpressures and polar and non-polar characteristics.

The primary fuel feed 2 is in particular composed of a mixture ofcomponents that can, in particular, consist of a mixture of hydrocarbonsthat can be subdivided into five primary groupings. The first group isthe heavy sulfur compounds (H Sulfur) 22 which are the multi-ringed andmulti-branched hydrocarbons with relatively high boiling points. Forexample, these include the di-benzothiophenes with boiling pointsgreater than 300° C. The di-benzothiophenes contain at least a threering structures and are aromatic compounds. The second group is thelight sulfur compounds (L Sulfur) 24, which are the simpler compoundscontaining sulfur with relatively lower boiling points and less thanthree ring structures. For example these include the various asmercaptans, thiophenes, and benzo-thiophenes with boiling points lessthan 300° C., and more preferably below 225° C. The third group is theheavy hydrocarbons (H HC) 21, and the fourth is the light hydrocarbons(L HC) 25, neither of which contain sulfur atoms which were included inthe first two groups. The fifth group is the additives 23, which arespecific to each type of fuel depending on the manufacture, themanufacturer, and other criteria. For example, military JP-8 fuel issimilar to commercial aviation fuel except that three additives arerequired in the specification. For JP-8 these are fuel system icinginhibitors (MIL-DTL-85470) di-ethylene glycol monomethlyiether(di-EGME), corrosion inhibitor/lubricity improvers (MIL-PRF-25017 andParadyne 655) and electrical conductivity/static dissipater (Stadis®450and MIL-S-53021). These specifications are set forth in the “GUIDE FORFIELD BLENDING OF ADDITIVES OR FOR WINTERIZING GROUND FUELS”,AMSTA-TR-D/210, U.S. Army Tank-Automotive Research, Development andEngineering Center (TARDEC), Warren, M148397-5000, October 1999,incorporated herein by reference in its entirety.

In the process 1 shown in FIG. 1, primary fuel feed 2 is separated intoan auxiliary fuel stream 3 and a return primary fuel stream 4 in amulti-stage process 1 consisting of a stage-one separation process 11and a stage-two separation process 16. The stage-one separation process11 supports the transfer through a membrane 12 of the lighter compoundsconsisting of light sulfurs 24 and light hydrocarbons 25, which exit asthe stage-one permeate 13. The other compounds 21, 22, and 23 areretained in the retentate stream 14 also resulting from the stage-oneseparation process 11. The stage-one permeate 13 is passed to thestage-two separation process 16. In the stage-two-separation processlight sulfur compounds 24 are selectively transferred through membrane17 along with some of the light compounds 26 as the stage-two permeate19 while most of the lighter hydrocarbons 28 are retained in thestage-two retentate stream 18. The stage-two permeate 19 is mixed withthe stage-one retentate 14 and returned to the primary application ortank as the return primary fuel stream 4. The stage-two retentate 18becomes the auxiliary fuel supply 3.

Although the stage-one 11 and the stage-two 16 processes are selectiveprocesses, their selectivity is not necessarily absolute. By controllingthe temperature of the feed streams 2 and 13 and the vacuum of thepermeate streams 13 and 19, the quantity of compounds actuallytransferred through the membranes 12 and 17 can be controlled.

The motive force for permeation is the partial pressure difference (PPD)of the compounds passing through the membranes in each stage. Thepermeation rate is enhanced as the temperature increases. Temperaturelimitation of the membrane materials may suggest a lower operatingpoint, but applying vacuum in the permeate side would give higher PPDmotive force to compensate for the lower temperature. As the temperatureof the feed stream is increased, the mobility of the compounds isincreased and permeability of the membrane is increased. Both parametersincrease the rate of transfer of compounds through the membrane. Thetemperature of the membrane also increases the vapor pressure ofcompounds exposed to the permeate side of the membrane.

In a process 1 using prevaporation membranes, a vacuum in a range of 1to 500 torr, and more preferably between 100 torr to about 200 torr, maybe applied to the permeate side and the compounds with the highest vaporpressure are evaporated from the surface of the membrane as a vapor. Theoptimal temperature range depends on the level of vacuum, the type ofprimary fuel, and the membrane material that is utilized. For example,where the primary fuel is an aviation kerosene and the light hydrocarboncut from the stage-one process 11 is in the gasoline boiling range, anda vacuum is applied across the membrane, then the temperature rangeshould be between about 100° C. and about 200° C., with a preferablerange between about 120° C. to 135° C. when a vacuum of 100-200 torr isapplied. If, on the other hand, the primary fuel is a diesel cut, thenthe temperature may be in the 150° C. to 300° C. range. The evaporationof the compounds with the highest vapor pressure creates a concentrationgradient across the membrane, which promotes the enhanced transfer ofthese compounds from the feed stream. Compounds with low vapor pressuresdo not evaporate and therefore, a concentration gradient is notestablished for these compounds and additional transfers do not occur.Other parameters such as the membrane surface area, membrane thickness,and internal fluid phase mixing on the retentate side of the membranealso contribute to the quantity of compounds transferred. Increases inmembrane surface area provide enhanced transfer because of the largerarea for transfer and the larger evaporative transfer area on thepermeate side. Thinner membranes have lower resistance for transport andsupport higher transfer rates because the concentration gradient that isestablished functions over a shorter distance.

The permeate flux is inversely proportional to the membrane thicknessand hence a thinner membrane is preferred if it can survive at theoperating pressure and temperature. Internal fluid phase mixing enhancestransfer rates by ensuring mixing of the various compounds in the feedstream and maintaining the highest concentration of high vapor pressurecompounds possible at the feed surface of the membrane. The masstransfer resistance in the bulk flow on the retentate side may reducethe effective partial pressure at the membrane surface. Turbulent flowor high flow velocities can improve mixing and increase flux. Adjustingthese characteristics of the membranes in stage-one separators andstage-two separators help ensure that all of the light sulfur compounds24 which are transferred in stage one 11 are again transferred in stagetwo 16. By operating at low enough temperatures where higher boilingcompounds do not vaporize, the amount of heavy aromatics or multi-ringsulfur compounds such as the di-benzothiophenes going through into thepermeate can be reduced and minimized.

The stage-one separation process 11 and stage-two separation process 16in accordance with the present disclosure can be carried out utilizing anumber of techniques ranging from flash vaporization separation (FVS),use of filtration membranes such as reverse osmosis (ROM),nano-filtration membranes (NFM) and ultra-filtration membranes (UFM) toprevaporation membranes such as non-polar prevaporation membranes (NPVM)and polar prevaporation membranes (PPVM). Proper selection of thespecific separation technique for each stage is dependent on thespecific primary fuel and the distribution of sulfur compounds withinthe mixture. The specific additives 23 and sulfur compounds in theprimary fuel feed 2 can also influence the selection of which separationtechnique is optimum.

The separation techniques suitable in the separation processes hereindisclosed, and their selectivity with respect to the compounds ofinterest in all embodiments of this process can be identified byconsideration of three characteristics. The first is physical size ofthe pores, the second is selectivity by polar or ionic characteristic ofthe compounds such as sulfur compounds, and the third is selectivity byboiling point or vapor pressure. One exemplary embodiment of the presentdisclosure involves a first step of separating a low boiling fractionpermeate for processing through a sulfur-selective membrane in a secondstep and collecting the light retentate as the clean product for downstream processes such as an auxiliary fuel source. The high boilingfraction retentate from the first step and the permeate from the secondstep are combined and sent back as the residual fuel.

Simple filtration processes such as ROM, NFM and UFM provide separationprimarily by physical size and structure. ROM separation devices haveeffective pores sizes below 0.0014 micrometers, while NFM devices havepores from 0.0008 and 0.005 micrometers and UFM devices have pores from0.0025 to 0.1 micrometers. These relate to compound selectivity bymolecular weight to some degree. For example ROM is good for compoundsbelow 300 gm/mole, NFM is good for between 160 to 10,000 gm/mole and UFMis good for between 2,000 and 200,000 gm/mole. In addition to mass, thethree-dimensional shape of the molecules also impacts selectivity withcomplex multi-ring structures having greater steric hindrances thanlinear straight chain compounds.

Separation technologies such as flash vaporizers and prevaporationmembranes are selective to the boiling point, or vapor pressure, of thecompounds. For example, in a flash vaporizer, a liquid feed ispressurized and heated. This heated and pressurized fluid is then passedthrough an orifice creating a rapid pressure reduction and evaporationof some of the low boiling point compounds within the mixture takesplace. Heavier compounds with higher boiling points remain as a liquid.Thus the fuel feed will then be a two phase mixture. This two phase(gas-liquid) mixture is then separated into a gas stream and a liquidstream. The gas stream is then condensed to complete the separationprocess. Utilization of a prevaporation membrane is similar, except, itcombines the separation processes of membranes and vaporization.

In one embodiment of a system in accordance with the present disclosure,a flash vaporizer equipped with a fractional distillation unit is usedas the first stage, and polar prevaporation membrane is used in thesecond separation stage. In another embodiment, polar prevaporationmembranes are used to perform both the first and second stageseparations. These PPVMs combine the physical filtration and polarselectivity to preferentially isolate polar compounds of small size, andthen apply additional selectivity because the transferred compounds thatare vaporized from the permeate side of the membrane. If a compoundphysically can transfer through the membrane, but its vapor pressure istoo low at the operating temperature to be vaporized, it will not becarried over to the permeate phase. Therefore, a PPVM separatoroperating at a defined temperature can demonstrate selectivity to bothlight hydrocarbons and light sulfur compounds.

In another embodiment of the system in accordance with the presentdisclosure, the stage-two separator has a greater selectivity to polarmolecules than the stage-one separator. This characteristic helps ensurethat all polar sulfur compounds and other ionic compounds, whichtransfer through the first membrane, are returned to the primary fuel byway of the second stage permeate flow.

An exemplary embodiment of the process is designed to provide alow-sulfur, clean fuel stream usable in an auxiliary power unit (APU)onboard a vehicle by extracting a fraction of the fuel being sent to theprimary application, such as to drive the engine or primary generator.An important parameter in the evaluation of the efficiency of theprocess is the ability to extract a low sulfur fraction of the fuelmixture while leaving behind substantially all of the fuel's performanceadditives and sulfur compounds in the return primary fuel stream.

FIG. 2 shows an embodiment of the process 1 of FIG. 1 implemented in asystem 60. In the system 60 primary fuel from the tank 61 is pressurizedby pump 63 in a primary fuel feed stream 32. The primary fuel feedstream 32 is then heated by the process recuperative heat exchanger 53to a primary fuel first hot feed stream 321. The primary fuel first hotfeed stream 321 is then heated by the hot engine fluid 50 in the heatexchanger 52 to a primary fuel second hot feed stream 322. This secondhot feed stream 322 is then fed to the stage-one separator 31 in whichit is separated into the stage-one retentate stream 37 and stage-onepermeate stream 34. The stage-one permeate stream 34 is then conveyedinto eductor 35 which is driven by the eductor's motive fluid 38. In theeductor 35, the stage-one permeate vapor stream 34 is put at vacuum,where the vacuum is due to the feed stream of eductor motive fluid 38.Exiting the eductor 35 is the combined liquid stream 36, which is amixture of the stage-one permeate stream 34 and the eductor motive fluid38. This combined liquid stream 36 flows to cooling heat exchanger 57where it is cooled. The weight ratio of cool motive liquid 38 tostage-one permeate vapor 34 is kept suitably high such that thecondensation heat raises the temperature of the combined liquid stream36 only slightly. The condensation of vapor into liquid results in lowervolume and thus a vacuum is created upstream. The use of an eductor withhigh velocity motive fluid also creates vacuum.

The hot liquid stream 36 is cooled in heat exchanger 57 into a coolliquid stream 360 which is increased in pressure by pump 137 and splitsinto motive stream 38 sent to eductor 35 and stage-two feed stream 42.Cooling unit 55 is a heat rejection element consisting of an air cooledor liquid cooled radiator or other appropriate mechanism such as thevehicle's air conditioning system through which excess heat can beremoved form the system. Cooling fluid streams 362 and 363 are coolingloops conceptually illustrated to transfer heat from the three coolingheat exchangers 56, 57, and 58 to the cooling unit 55. Although a seriesflow configuration is shown in the disclosure, it is not limited by thisillustration and any combinations of series or parallel flows andintegrated or dedicated cooling units are feasible and covered in thisdisclosure. Recuperative heat exchanger 53 transfers the heat fromreturn fuel stream 46 to feed stream 32. To ensure that all the vapor inreturn stream 46 is condensed cooling heat exchanger 56 is included.

A portion of the liquid stream 361 is passed onto the stage-twoseparator 41, as stage-two feed flow 42. In the embodiment shown in FIG.2, only a small part of the liquid stream 361 is passed onto thestage-two separator 41, while the most part flows to the eductor aseductor motive fluid 38. The use of liquid stream 361 as eductor motivefluid 38 eliminates the necessity of using a separate working fluid withits gas-liquid separators and dual downstream cooling heat exchangers.In steady state operations, the composition of the gas-liquid stream 36is primarily the light hydrocarbon and light sulfur compounds asdiscussed more in details below. In steady-state operation thecomposition of fluids 34, 36, 38 and 361 are the same that support thedirect condensation of gas-liquid stream 36 after it exits the eductor35.

The stage-two feed 42 is passed to re-heat heat exchanger 51 and becomesa hot stage-two feed 421 that enters stage-two separator 41. The feedstream of the hot stage-two feed 421 is separated into a stage-twopermeate stream 44 and a stage-two retentate stream 47. The stage-twofeed 42 may, in some alternative embodiments, first be heated throughrecuperative heat exchangers (not shown) interfaced with the outletstreams from stage two, either stage-two permeate 44 or stage-tworetentate 47 prior to entering re-heat exchanger 51. The sulfurselectivity of the membrane in stage-two separator 41 supports thetransfer of a majority of the sulfur compounds in the stage-two permeatestream 44 while maintaining some of the light hydrocarbon compounds asthe stage-two retentate stream 47 which is cooled and stored in tank 62as the auxiliary fuel supply. The better the selectivity of thestage-two membrane the more light hydrocarbons are retained in theretentate stream 47. The stage-two permeate stream 44 is put at a vacuumdue to the action of a motive fluid conveyed into an eductor 45. In thisembodiment, the motive fluid for eductor 45 is the stage-one retentatestream 37. In another alternative, stage-two feed 42 can be heated withone or more regenerative heat exchangers interfacing with the stage-oneretentate stream 37.

Use of the stage-one retentate stream 37 to drive the eductor 45minimizes the complexity of the process. Exiting from the eductor 45 isthe returning fluid 46 passing through the recuperative heat exchanger53 to improve process thermal efficiency. The fluid is finally passedthrough cooling heat exchanger 56 before returning to the tank 61 toensure the returning fluid is at or near ambient temperature.

One or both of the permeate streams may also be cooled in one or moreseparate cooling heat exchangers to enhance vacuum creation. In otherembodiments, the stage-one retentate stream 37 is cooled prior tofunctioning as the motive fluid for eductor 45. For example the eductor45 can be positioned downstream of recuperative heat exchanger 53 suchthat retentate stream 37 flows through heat exchanger 53 prior toentering eductor 45 as the motive fluid. In this embodiment, the motivefluid for eductor 45 is the stage-one cooled retentate stream 37. Inanother embodiment, one or both of the permeate streams are also cooledin one or more separate cooling heat exchangers to enhance vacuumcreation.

In other embodiments, exiting from the eductor 45, the sulfur compoundstransferred as permeate in the stage-two separator can be mixed with theretentate from stage one and returned to the primary engine or theprimary fuel tank 61.

The system disclosed above can be used to perform a multi-stageseparation process on board a vehicle to extract a low sulfur slipstream, in the stage-two retentate 47 of fuel compounds which can beused for auxiliary power units, while designing the separation stagessuch that performance enhancing additives in the primary fuel 32 areretained in the stage-one retentate 37 or returned to the stage-oneretentate by way of the stage-two permeate 44. In prior art andconventional approaches a slip stream of the primary fuel is removed asthe auxiliary fuel stream and then treated to completely destroy, adsorbor absorb the sulfur compounds.

This approach allows the extraction of a low-sulfur, clean fuel streamby way of a multi-stage process returning the sulfur compounds in theresidue to the primary fuel instead of adsorbing or absorbing them on toa throw away filter or a bed of solids and destroying the sulfurcompounds in the regeneration cycle. This approach also enhances theperformance of third stage adsorbents or absorbents, because the otherpolar compounds in the fuel are also reduced in concentration by thefirst two stages. Adsorbent storage capacity with the most commonly usedfuels was found to be one-tenth their capacity in comparison tosurrogate fuels which have been doped with specific sulfur compounds.This drop in capacity is due to other compounds such as additives orheavy aromatics, which are also polar in nature occupying active sitesfor adsorption.

One embodiment of the system focuses on using the retentate from stageone 37 as the motive fluid for the stage-two eductor 45 that providesthe vacuum on the stage-two permeate side. This retentate stream can becooled to enhance the performance of the eductor creating greater vacuumon the stage-two permeate side. Similarly, the evaporated permeatestream 44 can also be cooled and condensed prior to entering the eductor45 to further enhance performance. Also the stage-one retentate 37 canbe cooled prior to entering the eductor to further enhance vacuumperformance. Cooling of these fluids around the eductor can be throughdirect cooling or recuperative cooling in combination with preheatingfeed streams to the stage-one or stage-two membrane processes.

One embodiment of the system focuses on using the stage-one permeatestream 34 after condensation and pressurization as the motive fluid 38for the stage-one eductor 35.

One embodiment of the system focuses on the returning fluid 46 passingthrough the recuperative heat exchanger 53 to improve process thermalefficiency. The fluid is then finally passed through cooling heatexchanger 56 before returning to the tank 61 to ensure the returningfluid is at or near ambient temperature.

One embodiment of the system includes the use of the thermal energy fromthe primary engine application to provide the peak thermal energy needfor effective operation of the stage-one and stage-two separatormodules. This is illustrated in FIG. 2 with engine 50 and heatexchangers 52 and 53.

Another embodiment of the system process includes further integrationwith the primary vehicle. In this embodiment the cooling loop source 55is integrated with the vehicle's cabin air conditioning system tominimize component redundancy. Depending on the primary fuel type (suchas JP-8, diesel, or gasoline) the vapor pressure of the light compoundsin stream 34 and the pressure of the mixed stream 36 the temperatureneeded to fully condense the mixed stream 36 into liquid stream 361 maybe less than ambient temperatures. In this situation the cooling loopelement 55 may be integrated into the vehicle's air conditioning loopwhich has been designed to cool the cabin air. Alternatively, adedicated cooling unit capable of sub-ambient temperatures may be usedas cooling element 55.

The system and process represented in FIG. 1 and FIG. 2 have beenmodeled to assess the ability to effectively provide a clean, low-sulfurauxiliary fuel supply. FIG. 3 shows a diagram reporting the results ofthe performance of such a model. The model was developed assuming a feedfuel stream similar to JP-8 military fuels with 500 ppm of sulfur byweight. A typical JP-8 fuel has a boiling point range from approximately140° C. to 300° C. and is composed of multiple compounds: 57% paraffins,20% cycloparaffins, 20% aromatics, and 3% miscellaneous.

The data from the model was plotted on the chart with the y-axisindicating the sulfur content of the fuels. The x-axis is a measure ofthe type of sulfur compounds in the feed as represented by the relativesulfur concentration in the lighter fraction in comparison to the totalfeed. Therefore, a value of 100% indicates that the sulfur concentrationis uniform across the fuel's boiling point range. Detailed sulfuranalysis of several samples of Jet-A fuel with bulk sulfurconcentrations in the range of 1500 ppm to 3000 ppm has indicated that amajority of the sulfur compounds are relatively heavy, consisting ofdi-benzothiophenes type compounds. When a 30% light fraction is obtainedapproximately 70% reduction in the sulfur concentration is achieved,indicating a bulk fuel with 1500 ppm sulfur will produce a lightfraction with 450 to 500 ppm sulfur. This indicates the “relative sulfurin light fraction” is approximately 30 to 35% for typical Jet-A fuel,obtained from commercial sources in Long Beach, Calif. in 2005.Modifications in up-stream refinery processes may change thischaracteristic.

The feed concentration of the fuel is represented as the gray line 70and would be the concentration of the stream 32 of FIG. 2. The stage-oneseparator was modeled as a non-selective separation and 30% of the bulkfuel was extracted in the stage-one permeate 34 of FIG. 2. Since theseparation was not selective, the line with open circles 71 representsthe relative sulfur in the light fraction which, in this case, is 30% ofthe bulk fuel.

The stage-two separation extracted 40% of the feed stream 42 as permeate44 and achieved a selectivity which removed 98% of the sulfur in thefeed. This data is consistent with published performance data from W. R.Grace's PPVM modules for benzo-thiophenes and lighter sulfur compoundsin an intermediate cut naphtha fuel stream (Zhao X., Krishnaiah G., andCartwright T.; Membrane Separation for Clean Fuels; PTQ Summer 2004) thecontent of which is incorporated herein by reference in its entirety.

The performance of the stage-two separation is illustrated as the opensquare line 72, which indicates that sulfur levels of under 10 ppm areachievable if the relative sulfur in the light fraction is less than60%. If the required sulfur level in the auxiliary fuel is under 10 ppmor the relative sulfur concentration greater than 60%, a third stage maybe needed. In this example the stage-two retentate 47 was furthertreated with a liquid-phase sulfur adsorbent or absorbent in athird-stage adsorbent or absorbent module, which achieved a 95% removalperformance. The resulting concentration of sulfur in the product streamis represented by the open triangle line 73 that illustratesconcentration levels less than 2 ppm across the complete range ofrelative sulfur levels in the light fraction.

Further embodiments of the process and system can include the additionof this third stage adsorbent or absorbent module to polish the finalauxiliary fuel stream. FIG. 4 shows an exemplary implementation of suchembodiments. With reference to FIG. 4, the system is identical to thatof FIG. 2 except that a sorbent-type polishing filter bed 147 is addedto the process system in the stage-two retentate stream 47. If the downstream applications for the slip stream require very low sulfurconcentrations then the polishing filter bed 147 is added. Sulfurcompounds in the stage-two retentate are trapped in the sorbent-type bedsuch that the stream 148 leaving the bed 147 has very low sulfurconcentrations similar to the model results presented as line 73 of FIG.3.

The polishing filter bed 147 may be an adsorbent similar to high surfacearea carbon or carbon with specific surface modifications tailored toadsorbing the polar sulfur compounds. The bed 147 may be an absorbent orreagent designed to react with the sulfur atom in the compoundsresulting in a non-soluble sulfur inorganic salt that is trapped in thebed.

In summary, the present disclosure relates to a multi-stage process forthe separation of a slip stream of fuel with low-sulfur concentrationfrom a primary multi-component fuel stream. The primary multi-componentfuel is fed to the first stage in which a slip stream is isolatedcontaining lighter components and the heavier components are retained inthe retentate stream. The lighter component slip stream is furtherprocessed by the second-stage membrane in which the sulfur components ofthe slip stream are selectively removed from the feed as second-stagepermeate and a second-stage retentate is recovered as the low-sulfurauxiliary fuel supply.

In another aspect, the disclosure relates to a multi-stage process inwhich one or more of the stages are a selective membrane, and mostspecifically a polar or ionic, prevaporation membrane which has beendesigned to have selectivity for lighter sulfur compounds. Polymericmembranes such as Nafion (DuPont®), specially treated polyimides such asS-Brane (W. R. Grace) are examples of sulfur selective polarprevaporation membranes.

In another aspect, the disclosure relates to a multi-stage process inwhich one or more of the stages are a non-selective, high flux membrane.As with other preferred embodiments the stage-one permeate 34 iscondensed and fed to a second-stage membrane process 41. The high fluxmembrane is selected when the relative sulfur in the light fraction isless than 100%, as has been validated for some Jet-A type fuels.

As with any evaporation, distillation, or prevaporation process thespecies evaporating from the bulk fluid is driven by the vapor pressureof the individual species at the liquid gas phase interface establishedwithin the membrane. The vapor pressures of the individual species arestrongly dependent on the temperature, but all species have some finitevapor pressure, and therefore, as the light fractions evaporate traceamounts of the heavier species also evaporate. Depending on the specificsulfur compound species in the bulk fuel and the trace levels of thesespecies in the stage-one permeate 34 further refinements to thestage-one process may be needed to achieve an overall effective system.Another preferred embodiment of the system divides the stage-one processinto a stage-1A and stage-1B process. Both stage-1A and stage-1B areprevaporation, flux membrane, distillation, and/or evaporation typeprocesses. The permeate 34 stream for the stage-1A is condensed,reheated and sent as the feed stream to the stage-1B process. Thepermeate stream for the stage-1B is condensed and sent to the stage-twoprocess as previously described. This secondary stage-one process helpsto enhance the selectivity through dual filtering of the trace species.The retentate streams from both the stage-1A and stage-1B are returnedto the primary fuel tank.

Another exemplary embodiment of the system in accordance with thepresent disclosure addresses the issue of trace amounts of heavierspecies in the stage-one permeate 34. In this embodiment a two-stepcondensing function is integrated into the process after the stage-onepermeate stream 34 is created. FIG. 5 illustrates one preferredembodiment of this condensing function configuration applied to thesystems shown in FIGS. 2 and 4. Here, like numbers are used to designatelike elements previously discussed with reference to FIGS. 2 and 4.

The stage-one permeate 34 is passed through a partial condenser 370 inwhich the heaviest species are converted into liquid creating a twophase flow 381. The two phase flow 381 is passed into a gas-liquidseparator 372 creating a liquid stream 384 and a vapor stream 382. Theliquid stream 384 is returned to the primary tank 61 using a pump 373and a return connection 385. The vapor stream 382 is condensed in a heatexchanger 371 and passes to the eductor 35 by way of connection 383. Theprocess down stream of eductor 35 is similar to other embodiments of thesystem described above with reference to FIG. 2.

The multi-stage process in accordance with the present disclosure may beconfigured to have the pressurized retentate stream for the first stageflow through the motive side of an eductor to create a vacuum on thepermeate side of the second stage. In this configuration all permeatecompounds are returned to the primary fuel stream and the process isfurther simplified by eliminating the requirement for vapor liquidseparation hardware. Enhancements of this process and system can includethe cooling and/or condensation of the feed streams into the eductor 45to improve the vacuum performance creating a lower pressure for thestage-two permeate stream 44. This cooling function can be direct,through the integration of a heat exchanger connected to the coolingsystem 55, or can be achieved with recuperative heat exchangersinterfaced with other streams such as stage-two feed stream 42 prior toheating by heat exchanger 51, or with other streams such as stage-onefeed stream 321 prior to heating by heat exchanger 52. Other thermalrecuperation aspects and flow configurations are feasible to enhanceprocess energy efficiency and the embodiments of this process are notlimited by the configurations that have been illustrated for simplicity.

A multi-stage process in accordance with the disclosure may beconfigured such that the condensed permeate of the first stage flowsthrough the motive side of an eductor to create a vacuum on the permeateside of the first stage. In this configuration the process is furthersimplified by eliminating the requirement for vapor liquid separationhardware. In yet another aspect, the disclosure relates to a multi-stageprocess in which the thermal energy in the mixture of the first stageretentate and the second stage permeate is recuperated and transferredto the first stage feed to minimize thermal energy requirements.

A multi-stage process in accordance with the disclosure may beconfigured such that the peak thermal energy is provided to the stagesthrough integration with the reject heat from the primary engine in avehicle. The thermal cooling energy may be provided to the stagesthrough integration with the vehicle's vapor compression systemtypically used to condition the air within the vehicle's cabin.

In yet another aspect, the multi-stage process may be configured suchthat membrane systems are used to extract a low-sulfur slip stream whichis later used in a fuel cell or hydrogen generation system. For example,the initial stage membrane systems may also be integrated with a lastpolishing stage consisting of absorbent or adsorbent materials designedto extract the sulfur compounds to levels below 10 ppm concentrations.

The following modeled examples 1 through 4 are provided to describe thedisclosure in further detail. These modeled examples, which set forth apreferred mode presently contemplated for carrying out the disclosure,are intended to illustrate and not to limit the disclosure.

Example 1 Auxiliary Clean Fuel Stream for a 2-10 kW APU

Trucks and HumVee type vehicles use varying quantities of diesel orlogistic fuel (JP-8) depending on the speed, load being carried, andother parameters. Usually the main engine needs to operate even duringnon-drive time to supply heating or A/C or communication power needs. Inorder to improve the overall fuel efficiency and to reduce the timesmain engine needs to be operated, the heating and air-conditioning andnight-watch communication power may be supplied by a fuel cell operatingon hydrogen that will be generated using a low-sulfur clean fuel(approximately, 5 to 15% of the bulk fuel) separated from the primaryfuel.

Making reference also to the diagrams illustrated in FIGS. 1, 2 and 4,primary fuel from fuel tank 61 having a sulfur content of 500 ppm ispumped to 100 psig and sent to heat exchangers 53 and 52 where itstemperature is raised to 250° C., and then fractionated, separated orpartially vaporized in unit 31 by letting down to ambient pressure. Thevapor stream or permeate stream 34 is condensed (about 25% of feed byvolume) by mixing in an eductor unit 35 with condensed recycle stream38. The condensed light hydrocarbon stream contains about 400 ppm byvolume of sulfur but is free of additives and contains only traceamounts of higher boiling hydrocarbon components. Then the condensedlight stream 42 is sent to an exchanger 51 and to membrane separator 41,where it is split into a liquid retentate stream 47 and a vapor permeatestream 44, which is combined with the heavy stream 37 from unit 31 andreturned back to primary fuel tank as stream 45 containing about 550 ppmsulfur and all of the additives. The stream 47 contains less than 9 ppmsulfur and is the clean auxiliary fuel that is used in APU reformers(not shown here) for making syngas or hydrogen for use in fuel cellsthat produce electric power.

Example 2 Auxiliary Fuel Containing 1 ppm or Less

Where some reformers may need auxiliary fuels that contain 1 ppm or lesssulfur, then another separation (like unit 147) is added as describedbelow and illustrated in FIG. 4. The retentate stream 47 is passedthrough separator 147, which is a polishing stage that absorbs andretains the remaining sulfur species. Ultra clean retentate with lessthan 1 ppm sulfur is generated as stream 148 and cooled if necessary inunit 58 and stored in the clean auxiliary fuel tank or used by the APUreformer system (not shown here).

Example 3 Auxiliary Clean Fuel for APUs in Aircrafts

Currently commercial and civilian aircrafts have APUs that are generally50 to 250 kW in size that use JP-8 fuel in combustion process at lowefficiencies and producing pollutants even when they are on the ground.These APUs can be converted to low or non-polluting hydrogen based fuelcells as discussed in Example 1, using auxiliary fuel generated from thebulk fuel in the aircraft.

Example 4 Auxiliary Clean Fuel for APUs on Ships

Naval ships and merchant marine vessels can also be equipped with theauxiliary fuel production and reformers and fuel cells producing cleanpower while these ships are docked at port, as taught in Example 1, butat larger capacities 250 to 750 kW scales.

The following examples 5 through 7 represent the results of experimentsactually performed rather than results of modeling.

Example 5 Flash Vaporizer-Fractional Distillation as the Stage-OneSeparator and Polar Prevaporation Membrane as Stage-Two Separator with20% Cuts in Both Stages

A Jet Fuel (JetA) sample containing 1530 ppm sulfur was subjected tofractional distillation and the distillates were found to contain thefollowing sulfur levels. The JetA fuel sample was analyzed using a gaschromatograph equipped with atomic emissions detector (AED).

TABLE A Sulfur distribution in distillate cuts Thiols, sulfides Thio-Benzo- Dibenzo- Total & disulfides, phenes, thiophenes, thiopenes,sulfur, Sample # ppm ppm ppm ppm ppm 10% cut 361 53 81 0 495 20% cut 43323 121 0 577 30% cut 530 30 157 4 721 30-100% 978 21 1031 25 2055 cutWhole 824 25 674 17 1530 JetA

The above Table A illustrates the characteristics of various cuts orsection of the bulk hydrocarbon fuel. The last row indicates the sulfurconcentrations of the bulk fuel defined as Whole JetA containing the1530 ppm sulfur level. Most of these sulfur species were identified aslight sulfurs such as thiols, sulfides, and disulfides (824 ppm) andheavier sulfurs such as benzo-thiophenes (674 ppm). The row identifiedas 10% cut represents the fraction of the fuel where only the lightestspecies are removed similar to a stage-one permeate, while the 20% cutrepresents the next fraction or the 10-20% cut which excludes speciesremoved in the 0-10% cut and left in the 20-100% cut. As indicated bythe values lighter fractions had less sulfur (495 to 721 ppm) than thebulk fuel (1530 ppm) indicating a relative sulfur in light fractionbetween 25% for the 10% cut and 50% for the 30% cut. Also the dataindicates that most of the heavy sulfur species, represented by thedibenzo-thiopenes, remained in the 30-100% cut which would be thestage-one retentate that would be returned to the primary tank.

The second distillation cut (0-20% by volume) having 577 ppm totalsulfur was preheated to 125° C. and passed through a stage-two membrane(SB4034.4) that was maintained at 125° C. and at 26″ Hg vacuum. Permeatefrom the second stage (at a 20% stage-cut) contained 1130 ppm totalsulfur and the retentate from stage two contained 500 ppm total sulfur.The total sulfur reduction after stage one is 62% and the total sulfurreduction after stage two is 67%. The gasoline range sulfur, which isdefined as sulfur in compounds boiling below 220° C. (4280 Fahrenheit),is reduced from 200 ppm in stage one product to 120 ppm in the stage-tworetentate. This test indicates preliminary data that supports theeffectiveness of the concept but additional selectivity will be neededfor most practical applications.

Example 6 Flash Vaporizer-Fractional Distillation as Stage-OneSeparation and Polar Prevaporation Membrane as the Stage-Two Separationwith 9% Cut in Permeate Stage-One and 25% Cut in Stage-Two Separation

A Jet Fuel sample was analyzed using gas chromatograph equipped withflame photometric detectors (PFPD). Table B below indicates the sulfurspecies for both the whole jet fuel and for the 9% cut obtained from thestage-one permeate. The sulfur species are shown in greater detail andhave been organized within the table with the lightest species at thetop of the table and the heavier species at the bottom of the table. Asubtotal is provided for the sulfur species typically found in thegasoline fuel fractions indicating the light sulfur species of interest.As indicated by the data the relative sulfur in light fraction wasapproximately 40% (611 ppm/1473 ppm). The 9% cut also illustrated theelimination of a greater fraction of the heavy sulfur species, thoseabove the gasoline range.

TABLE B The 9% cut sample from fractional distillation (1^(st) stage)whole jet 9% cut Mercaptans 3 4 Thiophene 1 1 MethylThiophenes 2 3TetrahydroThiophene 1 1 C2-Thiophenes 3 13 C3-Thiophenes 23 67C4-Thiophenes 146 167 Thiophenol 3 5 MethylThiophenol 6 9 SubtotalGasolineRange S 188 270 BenzoThiophene 34 7 C1-Benzothiophenes 257 157C2-Benzothiophenes 362 109 C3-Benzothiophenes 488 68 C4+-Benzothiophenes141 0 Dibenzothiophenes 3 0 Total S, ppm by wt 1473 611

In stage two, the 9% cut distillate was preheated to 125° C. and fed tostage-two membrane maintained at 125° C. and 26″ Hg vacuum. The permeatefrom stage two (at a 26% stage cut) contained 710 ppm sulfur and theretentate contained 427 ppm sulfur, again indicating the sulfurselectivity of the stage-two prevaporation membrane. The gasoline-rangesulfur is removed selectively by the stage-two prevaporation processthrough the membrane, whereas the higher boiling sulfur compounds arenot reduced effectively. It is therefore preferable to get a lighterdistillate cut that eliminates more of the trace heavy sulfur species atthe stage-one separation process for more effective, overalldesulfurization process.

Example 7 High Flux Prevaporation Membrane with Two Step Condensation

This example pertains particularly to FIG. 5 in which two condensers 370and 371 are utilized. The JetA fuel sample was sent through a high fluxmembrane at 120° C. and 26″ Hg vacuum functioning as a stage-oneprocess. The stage-one permeate 34 was partially condensed into a liquidstream 384 and a vapor stream 382 further helping to separate the heavycompounds from the light compounds. Here, further removal of heavy, highboiling sulfur compounds were rejected from the stage-one permeate 34 byuse of the partial condenser 370. A 20% stage-one cut (20% of feed waspermeate 34 and 80% of feed was retentate 37) was extracted as permeate34, and the sulfur composition results are provided in Table C below asstage-one permeate without the partial condensation. The data indicatesthat the relative sulfur in the permeate 34 was less than 15% of theoriginal sulfur concentration (181 ppm versus 1473 ppm). Although thisdata indicates a substantial reduction in the sulfur compounds with thestage-one evaporation, some of these components, those identified belowthe subtotal defined in Gasoline Range S of Table C, are very difficultto remove in the stage-two 16 process as indicated in FIG. 1 above. Thispresents an issue that must be addressed.

TABLE C High Flux membrane as Stage-one with JetA fuel Sulfur Compounds(first 9 are lighter or gasoline range sulfur Stage-one Stage-onepermeate compounds and last six are feed (whole without partial heaviersulfur compounds) jet fuel) condenser Mercaptans 3 4 Thiophene 1 1MethylThiophenes 2 3 TetrahydroThiophene 1 1 C2-Thiophenes 3 13C3-Thiophenes 23 40 C4-Thiophenes 146 48 Thiophenol 3 4 MethylThiophenol6 8 GasolineRange S 188 122 BenzoThiophene 34 1 C1-Benzothiophenes 25715 C2-Benzothiophenes 362 43 C3-Benzothiophenes 488 C4+-Benzothiophenes141 Dibenzothiophenes 3 Total S, ppm by wt 1473 181

To address this issue, the partial condenser approach illustrated inFIG. 5 is incorporated into the stage-one 11 process. The stage-onepermeate 34 is cooled by a heat exchanger 370 only partially such thatonly the heaviest of compounds are condensed and the lightest compoundsremain in the vapor state so that the exit stream 381 is part vapor andpart liquid. This exit stream 381 enters a separator 372 in which theliquid phase or heavier compounds exit as liquid stream 384 and thevapor phase or lightest compounds exit as vapor stream 382. The lightestcompounds in the vapor stream 382 are further cooled in heat exchanger371 until all of the components are condensed and exit as liquid stream383. Now in reference to FIG. 6, a comparison of the distillation curvefor the lightest compounds of liquid stream 383 are illustrated by line390 and the heaviest compounds of liquid stream 384 are illustrated byline 391.

A sulfur analysis of the partial condensation process above-describedwas completed and is presented in Table D. The sulfur concentration inthe stream 384, or heaviest of compounds (Heavy condensate), and stream383, or lightest compounds (Light condensate), are defined. It wasdiscovered that the light condensate stream 383 contained no heavysulfur. The heavy sulfur compounds were condensated and contained instream 384, which are returned to the tank.

TABLE D Two-Stage Condenser for Stage-one Permeate Sulfur Compounds(first 9 are lighter or gasoline Stage-one Stage-one Heavy Light rangesulfur compounds feed Permeate Condensate Condensate and last 6 areheavier (whole before Stage-one (stream (stream sulfur compounds) jetfuel) condensers Retentate 384) 385) Mercaptans 3 4 3 0 8 Thiophene 1 11 0 2 MethylThiophenes 2 3 2 0 6 TetrahydroThiophene 1 1 1 0 2C2-Thiophenes 3 13 1 2 24 C3-Thiophenes 23 40 19 45 35 C4-Thiophenes 14648 171 93 3 Thiophenol 3 4 3 7 1 MethylThiophenol 6 8 6 15 1GasolineRange S 188 122 204.5 162 82 BenzoThiophene 34 1 42 2C1-Benzothiophenes 257 15 318 30 C2-Benzothiophenes 362 43 442 86C3-Benzothiophenes 488 610 C4+-Benzothiophenes 141 176 Dibenzothiophenes3 4 Total S, ppm by wt 1473 181 1796 280 82 Yield, vol. % 100 20 80 1010

The sulfur concentrations, as a function of boiling point for thevarious condensates, are illustrated in FIG. 7. In this figure data line394 represents the stage-one feed stream 321 or whole jet fuel as itenters the system shown in FIG. 5. Data line 393 represents the heaviestcompounds exiting the first partial condenser 370 and in the permeate 34as separated as stream 384 and data line 392 represents the lightestcompounds stream 382 of FIG. 5.

The Light condensate from the second condenser 371 was sent to thestage-two separator 41 or the sulfur selective S-Brane membraneseparator. The stage-two retentate 47 is recovered as the cleanauxiliary power fuel stream. The stage-one retentate 37 and stage-onefirst partial condensate stream 384 are combined with the stage-twopermeate 44 and sent back to the primary fuel tank.

This embodiment of the system, which utilizes two condensers in linewith the stage-one permeate, is illustrated in FIG. 8. The primary fuelfrom the tank 61 is pressurized by a pump 63 in a primary fuel feedstream 32. The primary fuel feed stream 32 is then heated by the processrecuperative heat exchanger 53 to a primary fuel first hot feed stream321. The primary fuel first hot feed stream 321 is then heated by thehot engine fluid 50 in the heat exchanger 52 to a primary fuel secondhot feed stream 322. This second hot feed stream 322 is then fed to thestage-one separator 31 in which it is separated into the stage-oneretentate stream 37 and stage-one permeate stream 34. The majority ofthe sulfur compounds are retained in the retentate stream 37 because,typically, a majority of the sulfur compounds are heavier than the lightfractions isolated as the stage-one permeate stream 34. This stage-onepermeate stream 34 in the vapor state can be treated by polishingfilter. The polishing filter may contain a catalyst where the sulfurcompounds are selectively converted to H₂S or SO₂ and SO₃ by addingeither H₂ gas or air respectively to increase the selectivity of theabsorption bed portion of the polishing filter or to enhancecondensation in the first partial condenser. The catalyst system can beheated to temperatures of 100° C. to 350° C. to improve reactivity.

The stage-one permeate stream 34 is then cooled by a heat exchanger 370only partially such that only the heaviest of compounds are condensedand the lightest compounds remain in the vapor state so that thepermeate stream 381 is part vapor and part liquid. This stream enters aseparator 372 in which the liquid phase or heavier compounds exit asliquid condensate stream 384 and the vapor phase or lightest compoundsexit as vapor stream 382. The lightest compounds in vapor 382 arefurther cooled in heat exchanger 371 until all of the components arecondensed and exit as liquid stream 383. This vapor stream 382 can betreated by passage through a polishing filter prior to entering thesecond partial condenser 371. The polishing filter may contain acatalyst where the sulfur compounds are selectively converted to H₂S orSO₂ and SO₃ by adding either H₂ gas or air respectively to increase theselectivity of the absorption bed portion of the polishing filter. Thecatalyst system can be heated to temperatures of 100° C. to 350° C. toimprove reactivity.

The liquid stream 383 is then conveyed into eductor 35 which is drivenby the eductor's motive fluid 38. In the eductor 35, the stage-one Lightcondensate liquid stream 383 is put at vacuum, where the vacuum is dueto the feed stream of eductor motive fluid 38. Exiting the eductor 35 isthe combined liquid stream 36, which is a mixture of the stage-one Lightcondensate stream 383 and the eductor motive fluid 38. This combinedliquid stream 36 flows to cooling heat exchanger 57 where it is cooled.

The hot liquid stream 36 is cooled in heat exchanger 57 into a coolliquid stream 360 which is increased in pressure by pump 137 and splitsinto motive stream 38 sent to eductor 35 and stage-two feed stream 42.Cooling unit 55 is a heat rejection element consisting of an air cooledor liquid cooled radiator or other appropriate mechanism such as thevehicle's air conditioning system through which excess heat can beremoved form the system. Recuperative heat exchanger 53 transfers theheat from return fuel stream 46 to feed stream 32. To ensure that allthe vapor in return stream 46 is condensed cooling heat exchanger 56 isincluded.

A portion of the liquid stream 361 is passed onto the stage-twoseparator 41, as stage-two feed flow 42. In the embodiment shown in FIG.8, only a small part of the liquid stream 361 is passed onto thestage-two separator 41, while the most part flows to the eductor aseductor motive fluid 38. The use of liquid stream 361 as eductor motivefluid 38 eliminates the necessity of using a separate working fluid withits gas-liquid separators and dual downstream cooling heat exchangers.In steady state operations, the composition of the gas-liquid stream 36is primarily the light hydrocarbon and light sulfur compounds asdiscussed more in details below. In steady-state operation thecomposition of fluids 383, 36, 38 and 361 are the same that support thedirect condensation of gas-liquid stream 36 after it exits the eductor35.

The stage-two feed 42 is passed to re-heat heat exchanger 51 and becomesa hot stage-two feed 421 that enters stage-two separator 41. The feedstream of the hot stage-two feed 421 is separated into a stage-twopermeate stream 44 and a stage-two retentate stream 47. The sulfurselectivity of the membrane in stage-two separator 41 supports thetransfer of a majority of the sulfur compounds in the stage-two permeatestream 44 while maintaining some of the light hydrocarbon compounds asthe stage-two retentate stream 47. The stage-two retentate stream ispassed through a sorbent-type polishing filter bed 147. Sulfur compoundsin the stage-two retentate are trapped in the sorbent-type bed such thatthe stream 148 leaving the bed 147 has very low sulfur concentrationswhich is then cooled and stored in tank 62 as the auxiliary fuel supply.

Polishing filters may optionally be located in the vapor-phase of thestage-one permeate stream, which may be heated to temperatures from 100°C. to 350° C. In one embodiment, the polishing filter may contain acatalyst where the sulfur compounds are selectively converted to H₂S orSO₂ and SO₃ by adding either H₂ gas or air respectively, to increase theselectivity and absorption capacity. H₂S or SO₂ and SO₃ are thenadsorbed in the polishing filters.

The complexity of sulfur compounds in liquid fuels is indicated by theinformation and species identified in the analyses above, and in facteach listing of species can be a range of individual compounds. Ingeneral the sulfur species can be separated into overlapping groupsbased on their chemical complexity and boiling point characteristics asshown in Table E below. The concentration of these species will varybased on the specific fuel and the refining process and feed stock usedfor the specific fuel. This variability makes developing an effectivedesulfurization process for auxiliary power applications difficult.

TABLE E Segregation of Sulfur Species and Compounds into Groups SulfurCompounds Group 1 Group 2 Group 3 Group 4 Group 5 Mercaptans X ThiopheneX MethylThiophenes X TetrahydroThiophene X C2-Thiophenes X XC3-Thiophenes X C4-Thiophenes X Thiophenol X X Methyl-Thiophenol X XBenzo-Thiophene X C1-Benzothiophenes X X C2-Benzothiophenes X XC3-Benzothiophenes X C4+-Benzothiophenes X X Di-benzothiophenes X X C2-Dibenzothiophenes X C3- Dibenzothiophenes X C4- Dibenzothiophenes X MoreComplex Species X

FIG. 9 provides a simplified conceptual flow diagram that outlines theoverall scope of the innovative desulfurization process and system ofthe present disclosure. FIGS. 10, 11, 12, 13, and 14 in turn illustratea number of different implementations of the process and system of thepresent disclosure.

Turning now specifically to the simplified system 600 shown in FIG. 9,the solid lines between components represent liquid phase connectionsand the dashed lines represent vapor phase connections, while heatexchanger, coolers, and heaters have been omitted to simplify theschematic representation. The elimination of these potential thermalintegration components is not intended to limit the overall scope of thedisclosure, but simply to facilitate ease of explanation at this point.

Feed fuel supply contained in tank 601 is separated and conditioned bythe innovative process of this disclosure into a low sulfur fuel forauxiliary applications. The processed low sulfur fuel is stored in tank602. Conventional approaches use an adsorbent or absorbent fixed bedthat removes the sulfur species and delivering the clean fuel, but withthe high concentrations of sulfur species these fixed beds can be largeand/or require frequent replacement or regeneration making this simpleprocess ineffective. The innovative process of this present disclosuregets around this inefficiency and ineffectiveness by selectivelyisolating specific sulfur species and returning them to the primary fueltank 601 and/or reacting the non-isolated sulfur species so that theyare easily isolated in downstream components.

In FIG. 9, liquid feed fuel from tank 601 is passed through connection610 to stage-one membrane separator such as separator 604. The lowboiling point fuel is extracted as a vapor from the feed fuel and passedto downstream components for additional processing through connection611. In this embodiment one of these downstream processes may be a vaporphase reactive desulfurization (RDS) catalyst reactor 607 followed by asecondary isolation component 608. The reactive desulfurization catalystreactor 607 uses a reactant entering the catalyst 607 through connection620. The reactant can be a oxidant such as oxygen, air, a peroxide,steam, or other highly oxidative reactant that will provide oxygen atomsto the catalytic reactor 607. These RDS techniques are defined as oxygendesulfurization (ODS) techniques, in which the vapor phase sulfurspecies are oxidized to form compounds of SO₂ or SO₃ (SO_((x))) that areeasily isolated on a sorbent bed(s). An example of a selective sulfuroxidation (SCO) catalyst is described by J. Lampert of EngelhardCorporation in J of Power Sources, Volume 131, Issues 1-2, 14 May 2004,Pages 27-34. The SCO catalyst is a precious metal catalyst supported ona honeycomb style monolith. The sorbent/trap for SO_((x)) is often mixedmetal oxides in a single bed or in two consequent beds one for SO₃ andanother for SO₂.

The reactive vapors can also be subjected to a reducing reaction usingreactants such as hydrogen, or other highly reducing reactant. These RDStechniques are defined as hydro-desulfurization (HDS) techniques, inwhich the vapor phase sulfur species are reduced to form hydrogensulfide or H₂S that is easily isolated on a sorbent bed, made up ofmetal oxides such as Zinc oxide or mixed metal oxides such asCuO/ZnO/NiO or even transition metal impregnated activated carbon orzeolites such as TOSPIX94. Typical vapor phase HDS catalysts areNickel-Molybdenum on alumina or Cobalt-Molybdenum on alumina.

The secondary isolation component can be a vapor phase sorbent bed 608(adsorbent or absorbent) and/or a membrane separator 605 and/or a liquidphase sorbent bed 606 (adsorbent or absorbent) depending on the specifictypes of sulfur species in the feed mixture and depending on thespecific types and quantities of sulfur species that are isolated in thestage-one permeate vapor phase 611 during the stage-one process. Each ofthese embodiments will be discussed in greater detail below.

In general and with respect to the sulfur species groupings defined inTable F, the stage-one membrane process is designed to eliminate speciesin the heavier groups, for example groups 3, 4 and 5. Based on thefeedstock characteristic (gasoline, kerosene, and/or diesel fuel cuts)in tank 601 and the mass flow ratio between stage one permeate 611 andthe feed 610, the effectiveness of isolating all of groups 3, 4, and 5will vary. As indicated in Table D above the stage one membrane 604 wasvery effective at eliminating groups 4 and 5 sulfurs, but still had over50 ppm of group 3 sulfurs. To eliminate these group 3 sulfurs a partialcondenser 603 is placed down stream. As a result the light condensate ofTable D, which represents the isolated fuel in connection 612 has verylittle group 3 sulfurs and consists primarily of group 1 and 2 sulfurs.

One approach would be to condense this vapor in connection 612 andprocess it by a second stage membrane reactor 605. Depending on theeffectiveness of isolating the group 1 and 2 sulfurs in the stage twopermeate 619 the final stage three sorbent bed 606 can be effective andnot require too frequent change outs or regeneration cycles. Thisapproach is outlined in greater detail with the discussion around FIG. 1to 5 set forth above. If the stage-two membrane process is not effectiveenough at isolating group 1 and 2 sulfurs the alternative embodimentwith the RDS catalyst 607 is needed.

FIG. 10 illustrates one more detailed preferred embodiment 500 of thisdesulfurization process system. Fuel in tank 501 passes throughconnection 531 to pump 511 to connection 532 and heat exchanger 512.Heat exchanger 512 provides heat to the fuel raising its temperaturebefore passing through connection 533 and into stage one membrane 504.The thermal energy used in heat exchanger 512 can be direct heat fromany primary source or can be recuperated heat from systems outside theprocess boundary such as the primary vehicle engine, or can berecuperated heat from within the desulfurization process boundary or canbe a combination of any of these sources. The fuel stream in connection533 enters the stage one separator 504 in which the fuel is isolatedinto a stage one permeate 534 and a stage one retentate stream 550. Theheavy sulfur groups are primarily isolated into the stage one retentatestream 550 and returned to the primary fuel tank. Only lighter sulfurgroups remain in the vapor permeate stream 534. Reactant is metered intothe system 500 through connection 560 and is mixed with permeate 534 andreacts on catalysts 507. The products of this reaction are sulfurspecies that are more easily isolated from the non-sulfur hydrocarbons.For example, they can be absorbed or adsorbed in sorbent bed 508 bypassing through connection 537. This yields a low sulfur fuel vaporstream. The low sulfur vapor stream exits sorbent bed 508 throughconnection 538 and is condensed in heat exchanger 515 into a low sulfurfuel liquid. Heat exchanger 515 can be directly cooled by an externalsource such as a chiller, a cold heat sink outside the vehicle likeambient air from an aircraft at high altitude, or any recuperativecooling source within the system 500 or by any combination of thesesources. The low sulfur liquid hydrocarbon auxiliary fuel then passesthrough connection 539 to pump 516 where it is pumped through connection540 to the auxiliary fuel storage tank 502. This embodiment is veryeffective if the light sulfur groups in permeate 534 are effectivelyreacted in catalyst 507 and absorbed or adsorbed in sorbent bed 508.

If the mass ratio of permeate stream 534 to feed stream 533 is high insystem 500, resulting in heavier sulfur groups in permeate stream 534,the addition of a partial condenser is potentially needed. A preferredembodiment 560 of the processing system that includes a partialcondenser 513 is illustrated in FIG. 11. In this embodiment 560 thevapor phase permeate 534 is partially condensed in heat exchanger 513and isolated in separator 509 after passing through connection 535. Thecondensed liquid stream with heavier sulfur groups are pumped throughconnections 551 and 552 by pump 514 and returned to the tank 501. Thevapor phase fraction of stream 535 is isolated by separator 509 andpassed through connection 536 to RDS catalyst 507. As in the previousembodiment the remaining sulfur species in vapor phase stream 536 arereacted with reactant from connection 560 on catalyst 507. These sulfurspecies are converted into sulfur species that are more effectivelyadsorbed or absorbed on sorbent bed 508.

Another embodiment 570 of the processing system is illustrated in FIG.12. If not all of the sulfur species in vapor steam 536 are reacted incatalyst bed 507 and isolated in sorbent bed 508, then a liquid phasesorbent bed is needed. In this embodiment 570 a liquid phase sorbent bed506 is added just before the auxiliary fuel supply tank 502 to ensurethat there is an acceptably low sulfur content in the feed streamthrough connection 543 of fuel being discharged into the auxiliary fueltank 502. Otherwise the system 570 shown in FIG. 12 is identical to thesystem 560 shown in FIG. 11.

In another embodiment 580 of the processing system, illustrated in FIG.13, the effectiveness of RDS catalyst 507 is limited to the heaviersulfur groups in vapor stream 534 and therefore, a high level of lightsulfur groups 1 and/or 2 are not isolated by upstream processes andremain in the liquid stream in connection 540. In this case a secondstage membrane reactor 505 can effectively be used to minimize oreliminate these groups from entering the liquid phase sorbent bed 506.

The liquid phase fuel in connection 540 is heated by heat exchanger 517and passed through connection 541 to membrane reactor 505. In membranereactor 505 a second stage permeate stream 553 and a second stageretentate stream 542 are isolated. The light sulfur species are isolatedinto the vapor phase permeate stream 553 due to the sulfur selectivityof the membrane. This vapor stream is condensed in heat exchanger 518and pumped back into the tank 501 by pump 519.

The auxiliary fuel stream is the retentate stream 542. Based on theperformance of second stage reactor 505, a polishing filter 506 may ormay not be needed. The low sulfur fuel stream is then passed viaconnection 543 to the auxiliary storage tank 502.

Another embodiment of the processing system 590 is illustrated in FIG.14. In this embodiment 590 both the partial condenser 513/separator 509and the second stage membrane reactor 505 are included. A separatediscussion of this embodiment 590 is not believed to be necessary, asthe features of this embodiment are simply combined from those ofembodiments shown in FIGS. 11-13.

Validation of the configuration presented in FIG. 11 was conducted andthe tested data is presented in Table F below. Two runs (18788-52A and18788-52B) were conducted with reactant 560 being hydrogen for ahydro-desulfurization process and the catalyst 507 was a commercial NiMotype. One test (921-3-4) was conducted with reactant 560 being oxygen(air) for a oxidative desulfurization process and the catalysts 507 wasa proprietary noble metal type catalyst. During all three tests thesorbent bed 508 was a high surface area activated carbon type bed. Thedata presented represents the concentration of sulfur species in stream539 after condensation. The data clearly indicates the sulfur reductioncapability of the embodiment defined in FIG. 11 with sulfurconcentrations under 15 ppm for test run 18788-52A.

TABLE F Test Data results from three runs with RDS and Partial condenser(FIG. 11) Test run Test run Test run 18788-52A 18788-52B 921-3-4 SulfurSpecies M1 lights with M1 lights with M1 Lights with Configuration HDSHDS ODS Mercaptans 0 0 0 Thiophene 0 0 0 MethylThiophenes 0 0 0TetrahydroThiophene 0 0 0 C2-Thiophenes 0.1 0.4 6.4 C3-Thiophenes 1.23.6 31.0 C4-Thiophenes 3.4 7.8 27.3 Thiophenol 0 0 0 MethylThiophenol 00 0 BenzoThiophene 0 0 0 C1-Benzothiophenes 1.5 2.7 0.3C2-Benzothiophenes 2.6 6.5 0.0 C3-Benzothiophenes C4+-BenzothiophenesDibenzothiophenes 0.0 0.5 0.0 Total S, ppm by wt 8.7 21.5 73.2 (AED)Total S, ppm by wt 12.1 30.1 90.0 (XRF)

Shown in FIG. 2 is a stage-two feed 42 passed to re-heat heat exchanger51 to maintain and provide a hot stage-two feed 421 that enters astage-two separator 41. If the re-heat heat exchanger were to beeliminated or reduced in size and/or capacity the feed stream would cooland the hot functioning stage-two separator 41 would nor workefficiently, or at all, depending on the nominal temperature themembrane operates at. In the exemplary implementation shown in FIGS. 15and 16 a modules assembly 700 such as a stage-two separator is shown.The module assembly has a spiral configuration which is tightly packedas compared to a planar module (which is a different geometry moduleassembly which also may be used for stage-two separation see FIG. 17).

The module assembly 700 function is described in reference to thestage-two separator described in other exemplary implementation. A fuelfeed 702 (such as a hot stage-two feed) enters one end of the moduleassembly 700. The module outer covering 704 is a leak resistant casingwith adequate strength and heat resistance to contain hot feed andresist a vacuum the covering and internal elements may also be referredto as a module or a body. Inside the module 700 the fuel 702 passesthrough feed channels 706 with spacers 708. The spacers 708 may comprisea wire mesh, or other porous flexible materials are within the feedchannel. A membrane 710, which may be a separate layer or formed as partof a side of the feed channel 706 provide communication between the feedchannel 706 and a vacuum collection channel 718. Collection channelspacers 714 which may comprise a wire mesh, or other porous flexiblematerials are within the vacuum collection channel. The vacuumcollection channels are positioned around a perforated tube 716 wherebya vacuum is drawn in the vacuum collection channel 718 and theperforations 720 communicate with the exterior of the perforated tube716. The perforated tube 716 usually made of stainless steel, is wherepermeate 722 is withdrawn under vacuum after having diffused through themembranes 710.

Those of ordinary skill in the art will recognize that a scavenging gasmay be used to assist in the evacuation of permeate vapor. In use, afeed solution enters the module assembly 700 at an input end 723 and theconcentrate (or retentate) 724 which is the depleted feed solution exitsthe output end of the module 726 (see generally FIG. 2). One or moreheating elements 728 are also wrapped into the spiraled module 700during its construction. The heating elements 728 are an integral partof the module assembly. The internal heat provided by the heatingelements 728 can increase or maintain temperature of the hot feed acrossthe length of the module. The diffusion across the membrane of thepermeate is a temperature dependant process. The addition of heat, fromthe heating element, inside the module can increase efficiency of theseparation. A variety of temperature sensing elements (RTD,thermocouple, etc.) can be inserted into the module and used in a PIDfeedback type control strategy to modulate the power input to theheating element. The monitoring may take place with the portion of themodule (which may be a chamber or layer) through which the feed passes.

The diffusion across the separation membrane is temperature dependantthe measurement of heat at, on, or proximal to the membrane is alsodisclosed. A self-limiting energy input strategy such as using apositive temperature coefficient resistive material may also be appliedto control the heat added.

Illustrated in FIG. 17 is a plate and frame membrane module assembly 800the hot feed flow 802 enters a chamber 804, formed between a top plate805 and a bottom plate 806 (form a casing), through an inlet 807 of themembrane module assembly 800. An outlet 808 at the perimeter of themodule assembly provides an exit for the depleted feed solution 809.Inside the chamber 804 the membrane 810 directs the permeate 812 intoone pathway for collection visa vie a vacuum outlet 814 and theretentate exits as depleted fuel 809 through the outlet 808.

The exemplary implementation shown in FIG. 17, also has one or moreheating elements 820 integrated within the module 800. Types of usefulheating elements for an integrated configuration series or parallelinclude heating blankets, resistance heating such as a Kapton heater,manufactured by Omega Engineering (www.Omega.com), radio frequency (RF)and fluid filled cavities, such as those manufactured by Watlow, Tempco.One or more spacers 822 are sequenced to provide separation for feedflow between the heating element(s) 820 and the membrane 810 as well asbetween the membrane 810 and the top of the chamber 802 in the top plate805. Alterations, changes, and additions may be made in the abovesystems and processes without departing from the scope of the disclosureherein involved. It is therefore intended that all matter contained inthe above description, and as shown in the accompanying drawing, shallbe interpreted as illustrative, and exemplary. It is not intended thatthe disclosure be limited to the illustrated embodiments.

While the apparatus and method have been described in terms of what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the disclosure need not be limited to thedisclosed embodiments. It is intended to cover various modifications andsimilar arrangements included within the spirit and scope of the claims,the scope of which should be accorded the broadest interpretation so asto encompass all such modifications and similar structures. The presentdisclosure includes any and all embodiments of the following claims.

1. A method for adding heat to a feed liquid within a prevaporationmodule, said method comprising; integrating a heating element within thebody of a prevaporation module; passing a liquid feed into the module onone side of a membrane; adding a quantity of heat produced by theintegrated heating element to the feed liquid as it passes through themodule; and separating permeate from retentate by passing the permeatethrough the membrane within the module.
 2. The method of claim 1,wherein the heating element is selected from the group consisting of anelectrical heat blanket, a liquid heating media hollow foil, anelectrically inductively driven electrical conduit and a radio frequencydriven electrical conduit.
 3. The method of claim 1, wherein the heatwithin the module is measured during use and that measurement is used,at least in part, to adjust the quantity of heat provided by the heatingelement over time.
 4. The method of claim 1, wherein the heat of thefeed liquid within the module is measured during use and thatmeasurement is used, at least in part, to adjust the quantity of heatsupplied to the feed liquid, by the heating element, over time.
 5. Themethod of claim 1, the method further comprising applying a vacuum tothe module whereby the vacuum assists the with the removal of permeatefrom the module.
 6. A more heat efficient prevaporation modulecomprising: a casing; a chamber formed with the casing; layered materialincluding at least a membrane and a heating element within the casing;whereby the membrane selectively separates out a permeate from a feedfuel stream and the heating element adds heat to at least one of thefeed fuel membrane; a means to introduce feed fuel to one side of themembrane; a means to remove depleted feed fuel which did not cross themembrane; and a means to remove the permeate which crossed through themembrane.
 7. The device of claim 6, wherein the means to introduce feedfuel is an inlet line and the means to remove depleted fuel is an outletline.
 8. The device of claim 6, wherein the means to remove the subsetof the feed fuel which crossed the membrane is a vacuum line out.
 9. Thedevice of claim 6, wherein the heating element is selected from thegroup consisting of an electrical heat blanket, a liquid heating mediahollow foil, an electrically inductively driven electrical conduit and aradio frequency driven electrical conduit.
 10. An heat efficient spiralprevaporation module comprising: a casing; a chamber formed with thecasing; wound layers of material including at least one membrane and atleast on heating element within the casing; whereby the membraneselectively separates a subset of a feed fuel stream and the heatingelement adds heat to the feed fuel and membrane; an inlet to introducefeed fuel to one side of the membrane; an outlet to remove depleted feedfuel which did not cross the membrane; and an permeate collection outletto remove the permeate which crossed through the membrane.
 11. Thedevice of claim 10, wherein the heating element is selected from thegroup consisting of an electrical heat blanket, a liquid heating mediahollow foil, an electrically inductively driven electrical conduit and aradio frequency driven electrical conduit.
 12. A method for adding heatto a feed liquid within a layered module, said method comprising; fixinga heating element within at least a portion of a module body throughwhich feed liquid flows during use; selectively controlling the heatproduced by the heating element; and adding a quantity of heat producedby the heating element to the feed liquid within the portion of themodule body through which the feed liquid flows.
 13. The method of claim12, wherein the heat within the module is measured during use and thatmeasurement is used, at least in part, to adjust the quantity of heatsupplied over time by the heating element.
 14. The method of claim 12,wherein the heat of the feed liquid within the module is measured duringuse and that measurement is used, at least in part, to adjust thequantity of heat supplied to the feed liquid, by the heating element,over time.